Despite being ranked fourth in the world, Paula Badosa came into her quarter-final showdown with the red-hot Coco Gauff as the underdog, but she played like a favourite en route to a 7-6 (7-4) 6-2 victory.
Usually one of her stronger weapons, Gauff's serve was a liability on Friday, with six double faults in the first set alone to drop the opening frame despite breaking Badosa twice.
In the second set, while Badosa was converting 92 per cent (11-of-12) of her accurate first serves into points, Gauff's figure was down at 53 per cent (eight-of-15) as the Spaniard's return game was at its best.
Badosa will meet seventh seed Daria Kasatkina in the semi-final after the Russian beat Belarus' Aryna Sabalenka 4-6 7-5 6-0. The longer the match went, the less effective Sabalenka became with her ability to return serve.
In the first set, which Sabalenka won, she was successful in 53 per cent (19-of-36) of the points against Kasatkina's serve, and that number plummeted to 14 per cent (two-of-14) in the decider.
Third seed and Wimbledon finalist Ons Jabeur was eliminated by ninth seed Veronika Kudermetova 7-6 (7-5) 6-2, and she will meet unseeded American Shelby Rogers in the second semi-final after she defeated Amanda Anisimova 6-4 6-4.
Meanwhile, in Washington at the Citi Open, Emma Raducanu felt the effects of her gruelling match 24 hours prior as she went down 7-6 (8-6) 6-1 to Liudmila Samsonova.
On Thursday, Raducanu played in the longest two-set match of the WTA season as she eventually made her way through two tiebreakers against Camila Osorio in two hours and 49 minutes, and she ran out of steam after another tough tie-break against Samsonova.
Samsonova will play China's Xiyu Wang in the semi-final after another upset, knocking out fourth seed Victoria Azarenka in convincing fashion 6-1 6-3.
Estonia's Kaia Kanepi booked her place in the second semi-final after a 6-7 (4-7) 6-4 6-3 win against Anna Kalinskaya, where she will meet Daria Saville after the Australian got the better of Canada's Rebecca Marino 6-1 7-5.